1. Field of the Invention
The present invention relates to a disk clamping device, and in particular to a disk clamping device which is capable of preventing a slip of a disk when the disk rotates at a high speed by increasing frictional force acting on the disk.
2. Description of the Conventional Art
Recently, with a need of a mass storage optical disk as an information recording and reproducing medium, densification of a disk is in progress. According to it, improving a data access speed of a CD-ROM (compact disk-read only memory) or a DVD-ROM (compact video disk-read only memory), etc. of a desktop or a portable computer is on the move. For that reason, a disk clamping device rotating at high speed comes to the fore.
FIG. 1 is a perspective view illustrating a conventional disk clamping device, FIG. 2 is a sectional view illustrating a hub of a turntable of the disk clamping device of FIG. 1 taken along the line Axe2x80x94A, and FIGS. 3A and 3B are state diagrams illustrating states before and after mounting a disk onto the clamping device of FIG. 1.
As depicted in FIG. 1, the conventional disk clamping device includes a spindle motor 10 as a rotational power source of a disk 30, a turntable 20 installed to the spindle motor 10 and rotating, a plurality of clamping grooves 21 formed at a hub 25 centering around a rotational axis of the hub 25 of the turntable 20 at regular angles and intervals, a plurality of springs 22 and a plurality of balls 23 respectively installed inside each clamping groove 21 for clamping the disk 30, and a circular lubber plate 24 installed at the outside of the hub 25 of the turntable 20 and contacted to the bottom surface of the disk 30.
The operation of the conventional disk clamping device will be described as below.
As depicted in FIG. 1, in a disk driver structure such as a thin optical disk player, the turntable 20 rotates by a rotational operation of the spindle motor 10.
As depicted in FIG. 3B, when the disk 30 is mounted onto the turntable 20, the hub 25 of the turntable 20 is inserted into a centrical hole 32 of the disk 30, the outer circumference 25a of the hub 25 is tightly contacted to the inner circumference 31 of the centrical hole 32 of the disk 30, accordingly the disk 30 rotates together with the turntable 20.
Herein, as depicted in FIGS. 3A and 3B, each ball 23 applied an elastic force of each spring 22 installed inside each of the three clamping grooves 21 formed centering around the rotational axis of the hub 25 of the turntable 20 at regular intervals projects over the outer circumference 25a of the hub 25 and contacts with the inner circumference 31 of the centrical hole 32 of the disk 30 in order to clamp the disk 30.
In more detail, as depicted in FIG. 2, the three clamping grooves 21 are formed at the hub 25 at regular angles (about 120xc2x0) and intervals centering around the rotational axis of the hub 25, the plurality of springs 22 respectively inserted into the three clamping grooves 21 apply pressure to the plurality of balls 23, each ball 23 applies pressure to the inner circumference 31 of the disk centrical hole 32, accordingly the clamping operation is performed.
In the meantime, in the above-mentioned structure, because a clamping force of the disk 30, namely, a frictional force acting on the disk 30 is determined only by a push force of the spring 22 applied to the ball 22, when an inertia force of the disk 30 is larger than a clamping force of the spring 22 in a high speed rotation of the disk 30, a slip of the disk 30 occurs naturally.
In order to prevent the slip, the circular lubber plate 24 is installed onto the turntable 20 in order to increase the frictional force acting on the disk 30.
However, because the circular lubber plate 24 is made of lubber materials, hardness and surface roughness of the circular lubber plate 24 are varied according to temperature and humidity. Accordingly, when the turntable 20 rotates and speeds up according to the rotation and speed-up of the spindle motor 10, the disk 30 may move in a direction opposite to the rotation direction of the turntable 20 due to an inertia force.
In addition, when a spring force is increased in order to increase a clamping force, it is difficult to mount the disk 30 onto the turntable 20, if the disk 30 is mounted by applying a pressure, the disk 30 may be deformed.
In addition, if each spring force is different, when the disk 30 is mounted and rotated, a vibration occurs due to an increase of an eccentricity of the disk 30, accordingly it is impossible to read/write the disk 30 normally.
FIG. 4 is a graph showing a natural frequency in a stop of a disk.
As depicted in FIG. 4, a natural frequency of a disk is divided into a forward traveling wave mode and a backward traveling wave mode in a rotating system, namely, in a rotation of a CD-ROM drive, etc.
FIG. 5 is a graph showing a relation between rotation speed and natural frequency.
As depicted in FIG. 5, a critical speed is between 7000xcx9c8000 rpm in a (0, 2) mode in which a natural frequency is decreased according to an increase of a rotation speed (for example: an increase of a speed of a CD-ROM). The natural frequency is increased due to characteristics of a rotating dynamic system.
In addition, the natural frequency does not increase continually, at a very high speed a flutter occurs due to a ductility problem of a fluid (air) and a solid (disk), accordingly it is impossible to read/write a disk normally.
FIG. 6 is a graph showing a flutter phenomenon according to an increase of a rotation speed of a disk and a natural frequency.
As depicted in FIG. 6, it is possible to increase a speed of an optical disk player by increasing a flutter speed, it means data can be read/written faster.
Accordingly, a flutter speed can be increased by increasing a critical speed.
Therefore, in order to increase a critical speed, a clamping force of a disk has to be increased, for that a spring force is increased in the conventional disk clamping device, however it may cause a deformation of a disk by applying excessive pressure to the disk in order to mount it onto a turntable.
In order to solve above-mentioned problems, it is an object of the present invention to provide a disk clamping device which is capable of preventing a slip of a disk in a rotation at high speed by increasing a frictional force between a hub and the inner circumference of a centrical hole of the disk.
In order to achieve the above-mentioned object, the present invention provides a disk clamping device for a disk drive having a hub insertable into a centrical hole of a disk, which includes a clamping means formed at a hub of a disk and increasing a normal force acting on the inner circumference of the disk so as to increase a frictional force between the hub and an inner surface of the disk in order to prevent a slip of the disk in accordance with rotation of the disk.
Also, the present invention provides a disk clamping device for a disk drive having a hub insertable into a centrical hole of a disk, which includes a plurality of clamping grooves formed at the hub at regular angles and intervals centering around the hub in a radial direction, a plurality of springs respectively inserted into the plurality of clamping grooves, a plurality of balls respectively inserted into the plurality of clamping grooves, pushed toward the outer circumference of the hub by the plurality of springs and contacting to the disk when the hub is inserted into the centrical hole of the disk and a fluid filled inside the plurality of clamping grooves in order to increase a frictional force between the plurality of balls and the disk in accordance with a rotation of the disk and the hub.
Also, the present invention provides a disk clamping device for a disk drive having a hub insertable into a centrical hole of a disk, which includes a plurality of clamping grooves formed at the hub at regular angles and intervals centering around the hub in a radial direction, a plurality of springs respectively inserted into the plurality of clamping grooves and a plurality of balls respectively inserted into the plurality of clamping grooves, pushed toward the outer circumference of the hub by the plurality of springs and contacting to the disk when the hub is inserted into the centrical hole of the disk, wherein angles formed by an imaginary centrical line of each clamping groove contacts and an imaginary tangent line of the hub are less than an angle of 90xc2x0, and the end of each clamping groove at the outer circumference of the hub is regularly placed centering around the hub in a radial direction.